The invention concerns a portable, combustion engine powered cutting or sawing machine comprising a rear part with a motor housing with a combustion engine and an engine block with a crankcase, and a front part with an annular saw and a blade holder. The invention particularly concerns a cutting or sawing machine of the mentioned type with a rear operating handle on said rear part, and a power transmission which includes a driving belt and at least one drive wheel in the blade holder for the drive of the blade.
A portable, combustion engine powered cutting or sawing machine is previously known through U.S. Pat. No. 4,352,241. It is a characterising feature of that machine that the rear part of the machine, including motor, operating handle and control means on one hand, and the front part of the machine with the cutting blade on the other hand, are pronouncedly displaced laterally relatively to one another, which is most clearly obvious in FIG. 1 and FIG. 2 in the patent document. This arrangement has several drawbacks. Firstly, the asymmetrical position of the saw blade may cause side ways directed kickbacks, which may cause severe injuries. Secondly, the machine is difficult and uncomfortable to operate in many situations; in short it has considerable deficiencies from an ergonomic point of view. These and other drawbacks basically are due to the fact that the motor housing and/or those components which are required for a combustion engine powered drive, such as crank case, fuel tank, fly wheel with fan and magnets, starter, air intake for fan and for engine, and exhaust gas purification, etc. necessarily form a voluminous unit. In order that the total dimensions of the machine shall not be still more increased, the blade from practical reasons therefore has been laterally displaced, in spite of the drawbacks caused by this arrangement. This and other circumstances are the reason why combustion engine powered cutting machines with an annular saw blade, so called ring cutters, have not made any break-through on the market place.
The development instead has taken the course towards hydraulic motor powered ring cutters, and this is particularly true after a very small, but at the same time very efficient hydraulic motor was developed, which is particularly adapted to ring cutters; U.S. Pat. No. 5,381,723 and U.S. Pat. No. 5,347,812. A hydraulic motor powered cutter or sawing machine having an annular blade, a so called ring cutter, which satisfies very high functional requirements, including very high requirements as far as safety and good working conditions are concerned, as well as, from an ergonomic point of view, is described in SE-C-509 533 and SE-C-509 547.
Hydraulic motor powered cutting machines, however, have one deficiency; they need to have a hydraulic power pack. It is true there exist portable power packs with a hydraulic pump, which can be powered by a combustion engine or by an electric motor, but in many situations there is no hydraulic power packs available or it is not possible to have such mobile power packs. Typical situations of that kind are in connection with accidents, fires, and on remote places and also, more generally, in regions having a low developed infrastructure. It has therefore existed a long felt demand for a combustion engine powered ring cutter with features which from an ergonomic and safety point of view which are equally or at least comparably good as those of hydraulic motor powered ring cutters and with performances which also in other aspects are good or very good.
In the invention aims at satisfying the said demands. The demand as far as good ergonomic conditions is concerned inter alia implies that the machine shall be well balanced and have a generally slender design, particularly in comparison with the previously known combustion engine powered ring cutter, U.S. Pat. No. 4,352,241, but also as far as the safety is concerned, slenderness and a balanced design has great importance. A slender, i.e. a comparatively elongated and slim design, however, also may mean fragility. It is a purpose according one aspect of the invention to address also that problem and to provide a ring cutter which is slender but nevertheless has a design which is robust and has a high resistance to bending moments, including a good strength against forces in all directions, i.e. axial or frontal forces, as well as torsion forces upwards or downwards, and lateral.
These and other objectives and advantages of the invention can be fulfilled through what is stated in the appending patent claims and in the following description of a preferred embodiment.